Playing the bowl takes patience and concentration (and often more strength than my arms have due to my MS) but the reward is always worth the time and effort. Patience, first, concentration, second, and the gift I receive is a 'song' that is tuned to my heart.
It could be that you are trying to hard. I don't use any strength and I have to be careful not to make the bowl sing too loudly or it annoys the people around me, like the neighbors.
Try staying as relaxed as possible and allow your energy to flow up and out from your center down your arm and into the bowl. Remember, you have to put the energy into the bowl to get the energy out of it. Focused intent is more important than muscle power or how fast you run the stick around the outside rim. Try imigining the bowl filling with your energy to the point of overflowing. The overflow will come out as sound.
As for the MS, have you tried acupunture. My wife, Jennie, is an acupuncturist and has a great deal of success with her MS patients. She can't cure them, but she sure amazes their doctors with the results she gets. Her patients get a large ruduction in the frequency and severity of exacerbations, reversal of lesions, and functional improvement.
Not every acupuncturist can get these results. Many acupuncturists report little success in the treatment of MS, or other neurologic conditions. You need to find someone who is familiar with the disease and knows their stuff. Jennie is good enough that she gets MS patients refered to her by neurologists. However, I'm sure she can't be the only acupuncturist in the world who is getting good results in the treatment of neurological condtions.